German Patent 1,904,584 (Glass), published on Sep. 18, 1969 relates to a method and apparatus for producing a knot-free fabric. This known method avoids the formation of knots in the fabric in that a motion of the weft thread which contains a knot is initially inserted into the loom shed, but again removed prior to the beat up motion of the reed. The faulty or knotty portion of the weft thread is cut off on the inlet side of the loom shed, whereupon the cut off faulty portion is removed again out of the shed. A knot monitor is arranged along the path of the weft thread from its supply spool to the inlet end of the loom shed. The knot monitor automatically stops the loom in that instance in which the weft thread portion containing the knot has been completely inserted into the shed, but prior to the beat up. Depending on the type of fabric, the loom may be switched on again, either directly after the removal of the faulty thread portion, or after switching the reed back to nullify any part of a beat up motion. A program control is not involved in this type of conventional faulty weft removal.
This known method and apparatus has the disadvantage that additional measures must be taken for removing the faulty weft threat portion of the weft thread that has been completely inserted into the loom shed. These features increase the costs and require a respectively substantial control effort and expense, unless the operator is intended to manually remove the faulty portion of the weft thread, which is also not desirable because it increases dead times.
European Patent Publication EP 0,292,044 (Shaw), published on Nov. 23, 1988, discloses a weaving method and loom which aims at avoiding the weaving of thread irregularities into the fabric. The noncleaned thread is supplied to an air nozzle weaving loom by thread supply coils or so-called yarn packages. These packages contain threads with irregularities, such as thinner sections, thicker sections, knots, entanglements, and wads. These threads are monitored and those thread portions that do not meet a certain requirement are removed by means of devices which involve additional and substantial costs. Thereafter, further weft thread is pulled off the supply packages and if the pulled-off weft thread is recognized to be free faults, it is inserted into the loom shed by means of the weft thread insertion nozzle or nozzles. Where it is necessary to weave a fabric having weft threads of different colors, the effort and expense for the additional structural features for removing undesired weft thread sections becomes prohibitive. For example, if weft threads of eight different colors are to be used, it would be necessary to provide sixteen weft thread storage devices or packages, each requiring the respective additional equipment for the proper removal of faulty sections in each of the differently colored weft threads. Such a solution to the problem of weaving a knot-free fabric is economically not feasible.